Even as global health experts were nervously eyeing a new coronavirus that has caused more than 10 deaths, word has arrived that China may be facing a new threat from an influenza virus typically limited to birds. Currently, there have been nine confirmed infections that resulted in three deaths. However, there may be other infections that haven't come to the attention of health authorities, and the original source of the infections remains unknown.
This particular strain is called H7N9 (for more on the H/N nomenclature, see our influenza primer). It's typically confined to birds, although CNN notes that H7N9 has infected humans a number of times in the past. Those infections, however, have rarely resulted in deaths. According to the Associated Press, Chinese health authorities say this virus is infecting birds without causing obvious symptoms, making it harder to track than past avian flu outbreaks, notably the H5N1 flu.
The World Health Organization's FAQ on the outbreak indicates that there is no evidence so far that the virus can spread among humans. That said, there are a couple of worrying indications. Chinese health authorities have published the DNA sequence of the virus, and one flu expert contacted by the Canadian Press notes that some of the genetic differences between this H7N9 strain and other avian influenza viruses could be an indication that this virus has adapted to mammals. A different report from the Associated Press says that an individual who died from the virus had two children who also came down with severe respiratory illnesses.
Two other facts seem pertinent to the virus' spread. Of the individuals who have contracted it so far, only one is involved in the poultry industry. And Chinese health authorities have started testing some of the bodies of pigs that have been found in a river that feeds the local water supply. So far, the virus wasn't present in any of the ones tested.
To summarize what we know: not a lot. Although H7N9 is an avian influenza virus, it can be present in bird populations without causing any symptoms, making it difficult to even identify which populations to be screening. This particular virus may be partly adapted to mammalian growth as well, which opens up other options for its spread. So far, however, there's no indication that the mammal doing the spreading is a human.
To complicate matters further, the full extent of flu viruses within a human population are often difficult to track. If 90 percent of the people who carry it only end up with minor flu symptoms, they probably won't come to the attention of medical authorities. (This often inflates the initial fatality rates, which tend to drop once widespread testing reveals a lot of additional cases that weren't initially recognized as being anything out of the ordinary.) And new cases tend to occur amid a background of infections caused by the typical mammalian flu viruses.
At this point, there have been enough worrying signs that the Chinese medical establishment is undoubtedly engaged in widespread screening for the virus. The country as a whole is heavily invested in genomics and has past experiences with dealing with emerging viral risks. But it may take weeks for that testing to provide a clearer picture of where the virus originated and how it's spreading to humans. Until we have a clearer sense of that, the overall risk is hard to evaluate. We'll provide updates should any new information warrant it.
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